singmaster



J. A. SINGMASTER.

MANUFACTURE OF FRENCH 0xm. APPLICATION FILED MAR-3111920.v

1,372,462, Patented Mar. 22, 1921.

2 SHEETSSHEET j averlzead Tro Hey I Me1i1h Furnace m1; WeZZ j V- .K

L A. SINGMASTER.

MANUFACTUR QQF FRENCH OXID. APPLICATION FILED MAR-31,1920.

l ST QAGQ. Patented Mar 9 1921.

3 d 2 H S-seam 2.

' M 'JQOIIOO UOHQO 00| 001 W SWUMM 33313 amen Lu u "To all whom it may concern:

1 "Unites; stares; rates-r OFFICE.

, J MESARTHUR SINGIVIASTER, or remann ron", PENNSYLVANIA, ASSIGNOR TO THE,

' NEW JERSEY ZINC COTILPANY, 01 NEW YORK, N. Y., AiCORPORATION OF NEW messy, V

Be it known that I, J AMES A. Sineimsrnn,

a citizeno'f the United States, residing at Palmerton, jin thecounty 01" Carbon, State of Pennsylvanla, haveinvented certain new and useful Improvements in the idanui'a-c ture or FIQIICh OXlCl; and I do hereby ide- Clare thefollowing to be a -i'ull, clear, and

' enact description of the invention, such as Will enable others skilled in the art to Whichit e'ap pertains to make and use the same.

This invention relates to the production 7 of Frenchoxid"(. 6., zinc oxid) by the reh {tort volatilizing process.

in the production or retort volatilizmgprocess, it s the universal practice, inso far a's I am aware, to carry on the operation in an intermittent manner-,and

"to wearer-i each charge before the" next charge is introduced into the retort. As a result, the properties of the OXlCl produced vary with the composition of the spelter Y'charged into theretort, and it is diihcult to" obtain a ;un1f0rm product where consider able variations occur in the spelter so charged Where lead' is" present 111 the spelter n any considerable amount, the lead vvill either go over With the zinc and appear must beremoved from the retort and is then su table only for renielting.

'invthe zinc, oxid as an impurity, or it will remain behind in the retort ashes Where it Furthermore,

j this intermittent method 0'1? "operation re- 'thegoperation;"So also, such operation of sults in a limited production of French oxid,

since "the retorts can be operated attheir maximum capacity only a part or the time.

.This limitation is greatly increased Where,

as is the common practice, the spelter is charged into the retort in solid form and mustfbemeltedtherein and burugrht to'thej volatilizing temperature before the production of'the oxid can take place. This inter- ..mittent method of 'operation involves ire" quent cleaning of the retorts, While the re- "torts theniselveshotinfrequently. crack. or failand must be replaced, thus further (lecreasingvthe output of the furnace and in creasing thelabor and expense involved in the retorts is wasteful offuel, for the reason I that the retorts must be kept at the proper temperature during the time intervalbe- 'i tween the end oi one operation and the French oxid by the MANUFACTURE 0F OXID.

' Specification of Letters Eaten't. fatefli gd N13; 22 1921 Application filed March 31,1920. Serial n ore,

- now obtained from eachretort. Moreover,

the amount of spelter is not obtained from each retort all at once, but is, commonly obtained in successive portions at intervals several hours apart. WVhere the retorts are all chargedat the same time, say once every 24- hours, and the charge is orkedofl' gradually, the spelter 1s commonly drawnat the end of three successive per ods; first, after the early port-ion oi the operation, then after a further I v period of operation, and finally at the end of the operation; The spelter thus produced is not uniform in composition, but varieswith variations in the zinkiferous material charged into the retorts, as Well as with the time of the draw, 'whether near the beginning of the spelter-producing operation or near its end Spelter driven ofi during the early part oi theoperation may have a materially different composition from that of the final draw. Inasmuch as the draws are usually several'hours. apart and all oil the retorts are commonly drawn at about the same time, there is produced a considerable amount of spelter at intervals of several hours apart, and of composltion varying with the different draws; If the spelter is I cast into slabs, as is customary, the slabs will have a composition corresponding; to that 0t each draw. If these slabs are then used for charging into the volatilizing retorts, the

composition of the spelter so charged will be determinedby the composition of thespelter I of the particular slabs, and consequent variations 111 the operation of the retortswill result.

of the volatilizing retorts and correspondingly increased yields of oxid produced. The advantages of uniformity and increased production moreover are obtained with material economy in labor and fuel, and other advantages of operation, hereinafter referred to.

The present invention is based upon the discovery that greatly increased cl. ic ty of the distilling retorts, and corresponding]3 increased production of oXids from. the same retort capacity, can be obtained by carrying out the retort volatilizing operation in a substantially continuous manner, that is, by charging molten zinc or spel or into the retorts from time to time to make up for that which has been volatilized, and by maintaining a substantial body 0.. molten Zincin the retorts, to which the further amounts of molten zinc are added from time to time. The invention is based upon the further discovery that a material im ment in the process and in the iu1i1.o.i.=..iity of the product can be obtained, even where the spelter employed varies greatly in its composition, by maintaining a large body of zinc in a molten state, wherein its composition is substantially determined, maintained and equalized, in accordance with the grade of oxid to be produced, and drawing off the molten zinc therefrom for chargin 5 into the volatilizing retorts. The invention involves further features of improvement which, as well as the advantages of the in yention, ill more fully appear from the following description.

In the operation of the volatilizing retort, according to the present invention, a preliminary charge of Zinc or spelter, either in slab or liquid form, is charged into tl retort, and the retort is brought to temperature required for the volatilizi. operation. 'lhereafter, molt-en zinc is added to the retort from time to time to maize up for that volatilized. The molten zinc so added is advantageously preheated to a ten.- perature near the boiling point of the metal. so that it will 110L- greatly reduce the tem aer ature within the retort, and so that the Continuity of the process will not be greatly interfered with. In carrying out the operation in continuous manner, it is advan tageous to maintain a considerable body of molten Zinc in the retc so that the retort will operate at approx @tely its maximum working capacit and toe supply of molten zinc in the rotor f is replenished from time to time so that the amount will not be too greatly decreaser 'W'here the molten zinc charged into the volatilizing retort contains lead, this lead can be held back in the retort and prevented from any objectionable amount of volatilization by naintaining a suflicient excess of raise, that is by preventing the zinc ratio from falling too low, such as would result if the charge were entirely worked off. If a suflicient excess ofzinc is maintained, the lead will accumulate in the retort, and, when the lead has so accumulated. to such an extent as to interfere with the desired uniformity and purity of the product, the lead-containing residue is then Withdrawn from the retort. Accordingly, by operating in this way, that is, by maintaining a suilicient excess of molten zinc in the retort, a product of high purity and of great uniformity can be obtained even where the molten Zinc charged contains varying amounts of lead.

The molten :zinc charged into the volatilizing retorts may be molten zinc from the spelter furnace, where the composition. and purity of the spelter does not interfere with the uniformity of the product desired. Accordingly, at such times as the speltcr is drawn from the spelter furnace, a part of uiis molten spelter may be maintained. in a molten state and charged directly into the volatilizing rotorts. it is more advantageous, however, to provide a melting furnace and to introduce the spelter into such furnace where it is. subjected to the equalizing action characteristic of the process of the invention.

In the preferred practice of the invention, there is produced and maintained a supply of molten spelter or zinc in the form of a dominantpool wherein the composition is substantially determined, maintained and equalized, and the resulting equalized molten Line is then charged into the mlatilizin re- Slab spelter may be melted. in su rnace to pro ide the necessary body 1' "en zinc, spolter directly from the furnace may be transferred in a melting furnace and h equalization of its kept molten therein, C(JBIPOSll'JOIL.

, is't'erring the soelter directly from the spelter furnace to the ting turn-ace, toe s tr ke-l i desired temperature composition of the spelter, either from the s lter furnace or supplied in slab form, will be equalized in the n'zelti g furnace and excess of lead uated out. It is one of the imivantages of the low in lead and uniformity he produced from or which is relatively high in lead. or

ies c nsiderably in its lead con- 311 such spclter rocuced into the melting furnace and r aintained therein in a molten state, an lead is materially in excess about 1% will liquate out as metallic lead in bottom of the melting furnace can be withdrawn therefrom and thus recovered as metallic lead. Not

llltl only is the zinc thus freed from its excess lead, but the lead itself is recovered in a merchantable form. i The temperature at which the molten'zinc is maintained in the melting furnace can, of course, be varied, but it is of particular advantage maintain the molten zinc at a 'temperaturegnear the boiling point of the metal, so that, when introduced into the volatilizing retorts, it"will not materially .tained within the body of the volatilizing rew illustrating, ina conventional and -20f Fig.1; I p v p M Fig. 3.18. a vertical longitudinal section Q of oneofthe oxid furnaces;

"the Zinc is thus preheated to near its boiling point and is added in relatively small amounts to the body of molten zinc contort, the temperature of the resulting mixtially its normal rate.

The invention will be further illustrated by the following more detailed description Y "of; they preferred practice thereof, reference being had to the accompanyin' drawing d1agrammatic manner, a furnace construction adapt- ;ed forthe practice of the invention. In the accompanying drawings, Flgure 1 is a plan showing a suitable furnace arrangement; I Fig; 2 is a sectional. View Fig. his..aQvertical transverse section of i such furnace;

' e rt? as rail 3 extends from the melting furnace 1 {the . Fig. 5 isa;verticalsectional view of one oftl 'volatilizing t t and Fig. 6 is a, sectional view of one of the showing: the level of the charge therein.

. In Fig. 1a suitable form of melting furnace is indicated at 1, thesame being a rever-. bera'tory furnace of suitable construction .havinga dip" wellfEZ from which the molten e'en be dipped; An overhead trolley or 3, supported by brackets 4 from one of alls 0f the building, passes the melt-- irnace an'd supports a ladle therefrom. illustrated in Fig. a. This overhead .to' the oxid furnaces 7 and .8, and is supportedtherefrom by bracket 6 as illustrated in. 4r. The'arrangement is such that the v'ltlie"overhead; trolley to the furnaces 7 thevolatilizing retorts through the funnel '15Ias illustrated in Fig. 4Q

Each-of the furnaces 7 and Sha s a series of retorts therein, shown as 20 for each fui'nace; The furnaces illustrated are retaken on the line;

lid 8, and poured into one or another or] will be readily understood and suitably heat ed by the combustion of gaseous fuel. In the operation of these furnaces the supply of air and gas is reversed from time to time so that combustion takes place first from oneend of thefurnace and then from the othenand so that the waste. products of combustion serve to heat the regenerators alternately, in the usual way.

The retorts 9. as illustrated in Figs. 4, 5 and .55, have the usual dam 10 at one end, and the usual opening; 11 there-above, and are closed at theother end by a closure or luting 12, through which extends the pipe-13 for supplying the reducing gas. This pipe 13 has a door 14 through which the funnel v duced into the melting furnace 1 in a molten state, as drawn from the'spelter furnaces, or slab zinc is introduced into the furnace and melted therein. The furnace illustrated is a reverberatory furnace heated in i the usual way, as will be readily understood.

so that the molten zinc will be maintained therein at the proper temperature. As

: 7 above noted,- it is of advantage to maintain the molten zinc considerably above its melt- 10o ing point and at a temperature approaching I its boiling point, so that the molten. zinc in the .rolatilizing retortswill not be greatly chilled by the introduction therein of metal at a materially lower temperature. Molten zinc at a lower temperature can be intro duced into the volatilizing retorts, but .if this is done it will correspondingly reduce the temperature of the total amount of molten 'zinc in the retort and the production of oxid will be delayed until the com:

izing temperature. n

In the melting furnace ithe inequal ties in the composition of the molten zinc are posite charge has beeniraised to the vol atil- I a equalized and the molten zinc is main ta ined ate temperature appropriate forcharginpj into the -volatiliz1ng retorts. This IHOllVlDZ' furnace may, as above noted, be char l :In order to obtain the desired benefit from the dominant poolto maintaine 'l in the melting furnace, there should preferably be The furnace adrantagcousl; ot the "go so that the zinc will be v therein. \Vhere molten l into the 'i'urnace.

he heat which it y new to supaznounts 0 at as wil en a e desired ten'iperature. li' h 1e molten spe is not available, slab 1 .c can be 1 iinarily melted and then maintained a. zen state in a similar manner.

i e the zinc contains more than about 11/; or e 1 ed out as metallic lea be withdrawn, for example, from the tom of the dip w ll 2, and converted pig lead which thus nrw a 7 product of the operation.

The maintenance of a molten Zinc in the melting of advantage, not only i 0 LS ta: contains, and lb ply sucn maintain the mo l" 01 thus sired equalization ththe spclter charge therein, but the molten metal to be maintained in a molten state in an advantageous manner.

In the production of the French oxid. the retorts are exterlu lv heated to a temperature above i'olatilization point oi? zinc.

but below the volatilisatiou point of lead, iron, etc, and the retorts are kept :lilled with a reducing gas. for instance, ole producer gas introduced through the pipe 12-3. The introduction of this J feats pr oxidation of the zinc vapor and also a in sweeping out the zinc van/m as test as itis formed, thereby promoting its tori. ation. The zine vapor and the producer gas are allowed to combine with the oxygen of the air at the retort mouth, and the oxid thus duced is collected in the usual way.

In the apparatus illustrate" n the drawing, the molten zinc at the proper temperature and advantageously at a einperature near the boiling point of the is dipped from the dip well 2 into the ladle and conveyed by the overhead trolley to the retorts 9 into w ch it to be char-g d. The molten zinc charged into the retorts through the tunnel inserted through the ooor ll. of the pipe 13, as illustrated in Fig. l. The level of molten zinc in the retort should not be permitted to fall too low, and further amounts of molten zinc should be introuuced irom time to time to maintain a suitable level in the retort and a suthcient body of molten zinc therein. For example, in a volatiliaing which holds a charge oi about 22:3 pou of molten Zinc, and where the capacity of the retort is about 1000 pounds of Zinc per Ql hours, the retort can be charged at intervals of from two to three hours, and with -dditions of around to 120 pounds oi molten Zinc tor each retort, to make up for the metal that has volatilized since the preceding charging oil? the retort. In this manner the amount of molten zinc is maintai' with approximatel3- its maximum surtace a considerexposed for volatilization w able body of molten Zinc is in cont? 1 the walls of the retort and is exposed to the direct heating action thereof.

Referring to Fig. 6, it will be see that the molten zinc in the retort has a very substantial contact surface with the retort lls through which the heat is transferred. and that effective heating of the molten 1 the retort is thus secured. The re preferably filled to about the level ixuli in this ligure, and a substantial body of is maintained ly further additions so that the level does not fall too low and so that the retort will be operated at approximately its maximum working capacity. it is turthermore advantageous to maintain a considerable body of Zinc to prevent vol atilization of lead, as above pointed out.

When it becomes necessary to clean a retort and remove toe ashes or the residual molten metal therefrom, the closure 12 broken aw y to permit this cleaning operation. The retort can then be charged with broken up slabs of zinc, and the retort then closed by luting with clay or other material which will bake and "form a solid closure by the time the solid has melted. If the closure is of such a character that it will quickly set or will prevent. the escape of molten zinc, the molten zinc can be directly charged into the retort at the beginning of the operation.

By operating in the manner above described, it has been found that the producing capacity of the retort can be very greatly in creased. It has thus been found that a regular furnace which will consume about 150 tons of metal per month, that is, when the zinc is charged cold. into the retort, will consume as high 272 tons or higher per month of molten metal where the zinc is charged into the retort in a molten state and where the retorts are operated in substantially continuous manner according to the present invention. That is, an increase of around 7 or more in the capacity of the retorts and in the yield produced can be readily obtained in this way.

This greatly increased capacity and yield is due, as I-believe, to the following reasons:

heat ransfer through the retort wall. capacity of the retorts can therefore be maln- When molten zinc is cha ed at a temperaously there is an approximately constant The - tainedfat approximately the maximum 1 cj'apac1ty,-due to the large contact area between the molten zinc and the heated Walls :of the retort," which contact area is prevented from being too greatly reduced by "metal.

the addition offur'ther amounts of molten The continuous operation of the retorts furthermore avoids the'lost time invol-ved in the operation of the retorts man "intermittentmanner, avoiding thus the time required for completing the working off of the individual charges, in cleaningthe reforts, in recharging the retorts interinit- V tently, and 1n bringing each successive charge I tothe volatihzmg temperature.

l? The greatly increased capacity and yield obtainable bythe present invention are vaccomp'aniedbyhigh zinc recoveries and low operatmg cost. "The contmuity and umformi'ty of operation very materially prolong the life ofxthe. retorts, which in turn reduces the Zinc losses, inasmuch as the ifa lureof a'retort permits a large port1on or the charge contained therein to escape to theflaboratory 'of the furnace where it is oxidized and escapes with the gases of combastion to. the atmosphere and is lost. also, the retorts absorb 'a certain small it is necessaryto replace.

amount of metal from the charge, usually about 20 pounds per retort, and the prolongation of'the life of the retort correretort ashes is also materially reduced, as

compared with, the customary practice of withdraw ng the retort ashes before each new charge isintroduced, when operating intermittently.

The present invention presents the further advantage of increased economvand etficiency of fuel and in the'amount of labor required; The prolonged life of the retorts correspondingly reduces the labor required' in replacing them, with resulting economy .in labor as well as the cost in the retorts .themselves, while the loss of active furnace time because of renewals is likewise very ma teriallydecreased. When the retorts are operated in a continuous manner, according tofthe present invent1on, they requlre cleaning only at relatively long intervals, so that I the labor'required for this purpose is cor- Trespondingly reducedv Instead of charg-' charged therein.

ing-and cleaning the retorts twice in '24:"

hours, as is the common practice,'they need only be cleaned once in about every hours.

I The reduced amount of work required in cleaning and replacing the retorts and in the operation of the furnace makes it poss1ble for the furnace crew to work in a more flexible manner and with a more constant amount of work, so that more care may be aiven to the heat control and to other factors which will influence the capacity and *the recovery. Even the labor which is required in the practice of the present inventron is less arduous and less dangerous, and

does not require as great skill or as much exposure to high temperatures as with the intermittent processes heretofore commonly practised, while the present process provides more frequent rest periods. It has been found that the-labor required for a furnace" 'm the practice of the present invention is not any greater than that needed in the cus tomary operation of the furnace in an intermittent manner, notwithstanding the greatly increased capacity. r

The saving or economy in fuelconsumption resulting from the practice of the present invention as compared with the customary operation of the furnace in an interm itt ent manner, is due to various factors, including the follow1ng:The more eliicient heating of the zinc in the melting furnace, previously referred to; the better heat transfer through the retort walls when the retort is kept well filled with molten metal, or with a substantial body of molten metal therein; the materialreduction in idle retort time due to the continuity of the process; and the increase in furnace capacity. it very. considerable amount of heat is normally' required simply to keep the retorts at the proper temperature, even if no metal is V This loss is avoided in the practice of the present invention, due to the continuity of the operation. So also, in the working off of an individual charge, in the common intermittent method of operation, the efliciency of the retort decreases as the amount of metal contained therein decreases and as they active area of contact of the re maining small amount of metal with the retort walls is decreased. This decreased efficiency is avoided in the present process, and the time interval between the working off period of one charge and the beginning of the next volatilizing operation,irequired by withdrawing the ashes, recharging the retort, and bringing the retort to the volatilizing temperature, is likewise avoided, or reduced to a minimum.

It will thus be seen'that the process of the present invention is one having manyadvantages and onewhich marks a very mateoxid by the retort volatilizing process.

" rial improvement in the production of French iii It will be understood that certain of the improvements of the invention can be used either alone or in conjunction with certain 01'? the other improvements, and advantages obtained characteristic of the particular improvements so used. When used conjointly accorning to the preferred practice of the invention hereinbetore set forth, the process is one having increased advantage, as will be evident from the "foregoing description. The various novel features and improve ments of the invention are set forth in the appended claims.

I claim:

1. In the production or French oxid by the retort volatilizing process. the improvement which consists in carrying out the operation in a suhstantiallv continuous manner by charging molten Zinc into the retort from time to time while the retort still. contains molten zinc previously char ed to make up for that whi h has been volatilized.

2. In the production of French oxid by the retort volatilizing process, the improve meut which consists in maintaining a sub stantial body of molten metal in the retort and adding further amounts of Zinc thereto from time to time to make up for that which has been volatilized.

In the production of French otzid by the retort volatilizing process the improvement which consists in operating the retort in a substantially continuous manner and at approximately the ma imum working apacity oi the retort. by maintaining in the retort an amount of molten Allie approximating that of m ximum worlringcap ty, and adding further amolmts of zinc from time to time to make up for that which has heen volatilized.

t. In the production of French oxid bv the retort volatilizing process the improve ment whiz consi ts in char ing the zinc volatilizing retort with molten nin at a tempcrature near the boiling point of the metal.

In the production of French oxid bv the retort role-.tilizing pri'u-ess. the improvd meat which consists in charging the zinc olatilizinn' retort with molten zinrat a temperature near the boiling; point oi the metal. and o rating the veto: a suhstantially mntiiI-uous manner.

6. In the production oi French oxid bv the retort volatilizing process the improve-- ment which consists in charging the zinc volatilizing retort with molten zinc and maintaining the level ot the charge during the main portion or" the working or period at a level substantially corresponding to the maximum working capacity of the retort.

'7. In the production of French oxid'bv the retortvolatilizing process, the improvement which consists in charging the zinc volatilizing retort with n'uolten zinc at a temperature near the boiling point o'r the metal and maintaining the level of the charge during the main portion of the working oil period at a level substantially corresponding to the maximum workin capacity of the retort.

S. In the production oi French oxid by the votalizing of Zinc in a retort and the subsequent burning or oxidation of the volatilized metal on its issuance from the retort the improvement which comprises preliminarily forming and maintaining a dominant pool oi molten zinc of a composition appropriate to the grade of oxid to be produced, and drawing upon said pool to supply the retort.

In the production of French oxid by the volatilization of zinc in a retort and the subsequent burning or oxidation of the retort, the improvement which comprises liquating a body of molten zinc. adjusting the composition oi the molten mass in accordance with the grace o't oxid to be produced. and supplying the zinc in a molten condition to the retort, the composition of the molten metal charged being substantially by maintaining a doini 'zanl pool in the melting furnace sufiicient to guard against material fluctuations from minor differences in the con'iposition of the metal.

ll. In the production of French oxid b7? the volatilization of zinc in a retort and the subsenueiut burning or oxidation of the volatilized metal on its issuance from the retort the improvement which consists in maintaining in the Zinc volatilizing retort a considerable body of molten zinc and supplying further amounts of molten zinc thereto from time to time preheated to a temperature near the boiling point of the ottmolten zinc for charging the volatilizing retorts from. time to time, and charging; the molten spelter into the zinc volatilizing retorts.

'13; In the production of French oxid by the volatilization of zinc in a retort and the subsequent burning or oxidation of the volatilized metal on its issuance from the retort, the improvement which consists in maintaining in the zinc volatilizing retort a considerable body of molten zinc and adding thereto from time to-time further amounts of molten zinc, the composition of Q volatilized metal on its issuance tromthe retort, the improvement which consists in drawing off spelter from a spelter furnace, maintaining the spelter 111 amolten state and in the form of a dominant pool wherein its composition 'is substantially determined,

maintained and equalized, and charging the resulting molten zinc into the zinc volatilizin g retorts.

15. In the production of French oxid by the volatilization of zinc in a retort and the subsequent burning or oxidation of the vola- 1 tilized metal on its issuance'from the retort,

the'improvement which consists in charging molten z nc which contains lead into the volatilizing retort, maintaining an excess of zinc inthe retort to hold back the lead from volatilizing by adding further amounts of molten zinc from time to time, and finally V, withdrawing the residue rich inlead from y the retort.

16.; In the production of French oxid by the volatilization of'zinc in a retort and the subsequent burning'or oxidation of the volatilized metal on its issuance from the retort,

- theimprovement Which comprises maintain- .ing lead-containing zinc in a liquid state to permit the excess of lead to liquate out, and charging the resulting purified zinc into the volatilizing retort. j

17. In theproduction of French oxid by l the volatilization of zinc in a retort and the taining lead-containing zinc in a liquid state subsequent burning or oxidation of the volatilized metal on its ssuance from the retort, the improvement which consists in mainto permit the excess lead to liquate out,

, chargingthe resulting purified zinc into the volatilizing retort, maintaining an excess of zinc in the retort to hold back the remaining lead'from volatilization by adding further amounts of molten zinc from time to time,

and finallywithdrawing-the residue rich in lead from the retort.

18; In the production of French oxid bv the volatilization of zinc in a retort and the ti-lized zinc on its issuance from the retort, the improvement which consists in maintaining a substantial body of metal in the volatilizing retort and adding further amounts of metal from time to time, the composition of which has been equalized.

19. In the production of French oxid by the volatilization 0i": zinc in a retort and the subsequent burning or oxidation of the volatilized' zinc on its issuance from the retort, the improvement which consists in charging lead-containing zinc into the volatilizing retort, and maintaining an excess of zinc in the retort to hold back the lead from volatilizing by 7 adding further amounts of zinc from time to time, and finally withdrawing the residue rich in lead from the retort.

20. In the production of French oxid by the volatilization of zinc in a retort and the subsequent burning or oxidation of the. volatilized zinc on its issuance from the retort, the improvement which consists in charging lead-containing zinc into the retort and add ing further amounts of zinc from time to time to maintain a substantial body of metal in the retort and a sufiicient excess of zinc to hold back the lead from volatilizing, the body of-metal so maintained being suilicient to secure continuous and effective heat transfer through the walls of the retort to the body of metal so maintained.

21. In the production of French oxid by the volatilization of zinc in a retort and the subsequent burning or oxidation of the volatilized metal on its issuance from the retort, the improvement which consists in maintaining a body of lead-containing zinc in a liquid 7 state to permit the excess of lead to liquate out and to equalize the composition of the zinc, charging the resulting molten zinc in a preheated state into the volatilizing retort, maintaining a substantial body of molten zinc in the retort containing a sufficient excess of zinc to hold back the'lead from vola tilizing, supplying further amounts of molten zinc to the retort from time to time to make up for that volatilized, and finally withdrawing the lead-containing residue from the retort. I

22. In the production oi French oxid by the retort volatilizing process, the improvements which consist in maintaining a sub stantial body of molten zinc in the retort, drawing off spelter from a spelter furnace, and charging the spelter while still molten into the volatilizing retorts.

In testimony whereof I afiix my signature.

JAMES ARTHUR SINGMASTER. 

